The invention concerns a system for withdrawing small amounts of body fluid comprising a drive unit with a holding device for a disposable lancing unit which has a holding area and a capillary structure connected to the holding area. The capillary structure has at least one capillary channel and a tip for piercing the skin which faces away from the holding device. At least a part of the longitudinal extension of the capillary structure is open towards the outside.
Systems for withdrawing body fluids are already known in the prior art in which the body fluid is taken up into a disposable element. Blood collection and analytical systems are known from the document EP 0 199 484 which comprise a disposable unit with a capillary to collect body fluid and transport the body fluid into a detection area. The further development of this concept is described in WO 97/42888. The arrangement described herein is particularly suitable for collecting relatively small amounts of body fluids which is primarily accomplished by pressing a ring onto the area surrounding a collection site and a pumping movement. A system for analysis based on small amounts of interstitial fluid is known from EP 0 723 418. For this purpose a very thin closed hollow needle is inserted into the dermis and interstitial fluid is conveyed through the needle to a test zone by applying pressure to the area surrounding the puncture site. A highly miniaturized arrangement which also utilizes a closed needle to withdraw body fluid is known from U.S. Pat. No. 5,801,057. A particular advantage of this arrangement is the extremely thin needle which can be inserted at least into the arm region of a patient without essentially any pain.
Whereas the arrangement described in U.S. Pat. No. 5,801,057 already fulfils numerous practical requirements, some features are in need of improvement. A general problem with the sampling devices according to the previously mentioned document is to manufacture the hollow needle cost-effectively and as small as possible. Miniaturization which is in particular desirable with regard to minimizing the pain caused by the lancing process and minimizing the size of the puncture wound results in high manufacturing costs for the very thin closed needles and there are additional fundamental feasibility problems.